This invention relates to a document registration apparatus for use in a document reproduction machine in which different size original documents are placed on a transparent platen and an image projected along the optical centerline of the machine imaging system. From a human factors perspective, the optimum positioning for a document on the platen surface is to align a document edge along a corresponding corner edge of the platen. The projected image of the document, as formed on the photoreceptor, has a known center line on the photoreceptor which is then used as the reference point for the subsequent xerographic operations. It is desirable to maintain this center line irrespective of the size of the document to be copied or the specific magnification value selected.
FIG. 1 illustrates the problem encountered in copying documents of different sizes. The figure shows a top view of a transparent document platen 10. In a conventional manual document reproduction mode, a fixed registration edge or edges extend linearly along one or two sides of the top surface of a document platen. These edges provide either center or corner registration with two orthogonal edges of the document aligned with two orthogonal registration lines of the copier platen. This registration provides alignment of the original document with the optical system and copy sheet registration of the particular reproduction device employed. For a machine having the capability of reproducing documents of differing dimension, either at 1:1 magnification, or at a reduced or enlarged magnification, the position on the platen, document and hence the registration edges, must be changed to maintain the center line of the document aligned with the optical system centerline. This problem is illustrated by reference to FIG. 1 which shows a top view of a transparent platen 10 utilizing a pair of registration guides 12, 14 to provide a lower left corner registration edge 16. A letter size document 18 with a width of 81/2 " in the Y direction placed on the platen in the corner registered position, will have its center line CL(Y) coincident with the optical system centerline. However, as one example, if a larger size document, such as a computer printout 20 with a width of 101/2' in the Y direction is placed in the corner registration position, the centerline CL(Y') of this document will be 2" above the optical center line required, hence the latent image formed at a photoconductor surface will be misaligned.
It is therefore an object of the invention to provide a registration mechanism which is sufficiently versatile to accomodate changes on document size while maintaining optical alignment. This object is realized by providing in a document reproduction apparatus having a transparent platen for supporting a document to be copied, at least one document registration edge associated with said platen, a pivotable cover, and an optical projection system for projecting light images of said document from said platen to a photosensitive member, the improvement comprising: means for selectively engaging at least one of said registration edges with said platen cover whereby, upon engagement, said registration edge is moved from a position in optical alignment with said projection means to a position out of alignment with the projection means.